1. Field of the Invention
This invention relates to the field of manufacturing semiconductor wafers by techniques such as vapor deposition of films on substrates. More particularly, the field of this invention involves the vapor deposition of epitaxial films, for example single crystal films such as silicon films and amorphous films such as silicon dioxide films, on exposed surfaces of articles, such as single crystal silicon and non-crystalline wafer substrates commonly used in the electronics industry. Gaseous chemical reactants are brought into contact with a heated substrate within a reaction chamber the walls of which are transparent to radiant heat energy transmitted at a predetermined short wave length. A susceptor, which absorbs energy at the wavelength chosen, supports the substrate to be coated. In one preferred embodiment, the susceptor heats the substrate with energy absorbed from a radiant heat source. In other preferred embodiments, which are particularly suitable for use with single crystal substrates and/or films, both the susceptor and the substrate are heated directly and simultaneously by the absorption of heat energy transmitted into the reaction chamber from the radiant source.
2. Description of the Prior Art
While single crystal substrates, such as silicon wafers, and non-crystalline substrates have been coated heretofore with amorphous epitaxial films, such as silicon dioxide films, and with single crystal films, such as silicon films, so far as is known, the specific and improved vapor deposition procedure and apparatus disclosed herein are novel. The apparatus and process of this invention are effective to produce uniform film coatings on substrates under controlled conditions so that coated substrates with high quality and excellent film thickness uniformity are producible within closely controlled limits. Moreover, with single crystal substrates and/or films, little or no crystallographic slip is introduced into either the substrate or the film during processing.
In chemical deposition systems, it is highly desirable to carry out the deposition reaction in a cold wall type reaction chamber. By maintaining the reaction chamber walls in the unheated state, such walls receive little or no film deposition during substrate coating. Cold wall systems are additionally desirable because they permit the deposition of high purity films, such as silicon and silicon dioxide films. Impurities can be evolved from or permeate through heated reaction chamber walls. Because such impurities would interfere with and adversely affect the purity of the substrate coating, cold wall reaction chambers are employed to preclude such impurity evolution or permeation.
To avoid such problems, chemical deposition processes have been developed heretofore which permit heating of a substrate positioned within a reaction chamber without simultaneously heating the reaction chamber walls. Heretofore, the most successful of such processes involved the use of radio frequency (RF) induction heating of a conducting susceptor positioned within the reaction chamber, the walls of which were formed of non-conducting or insulating material. For example, RF heating of a graphite susceptor within a quartz reaction chamber for depositing epitaxial silicon films has been known generally heretofore. The RF energy used typically has a frequency on the order of 5 KHz to 500 KHz. p However, such an RF heating technique, while it generally produces the stated objective in a cold wall reaction chamber, has several inherent and important disadvantages which make the same undesirable under many circumstances. For example, an expensive and bulky RF generator is required which is very space consuming and which must be located close to the epitaxial reactor. Also, the high voltages required with the RF coils produce substantial personnel hazards, and RF radiation from the RF coils can and frequently does interfere with adjacent electrical equipment. Furthermore, such an RF procedure requires the utilization of an electrically conducting susceptor for supporting the substrates to be heated. Also, RF systems are considered more expensive overall than the simplified radiation heated system disclosed herein which were designed to replace the RF system utilized heretofore.
RF systems and other indirect heating systems in which energy is induced in a susceptor which in turn transfers heat to the substrates have another important disadvantage. Less than perfect contact between the substrates and the susceptor causes localized heating of the substrates and therefore generates significant thermal gradients in the substrates. With substrates fabricated of a single crystal material, the stress induced by the thermal gradients frequently exceeds the elastic limit of the crystal and is relieved by movement of crystal planes relative to one another. This mode of stress relief results in a crystal defect known as crystallographic slip. Such slip can be generated at a steady state condition as well as during wafer heat-up. If heating of the single crystal wafer is indirect, i.e. by transfer from a heated susceptor, and heat transfer to the wafer or heat loss from the wafer is not uniform, significant temperature gradients may exist in a direction parallel to the wafer surface at steady state. These gradients may arise from temperature gradients in the susceptor, variations in the spacing of the wafer from the susceptor, wafer bow, and/or variations in heat loss from the wafer.
Crystallographic slip might, to some extent, be eliminated by maintaining perfect contact between the wafers and the susceptor, by heating the wafers very slowly, or by making the wafers thicker or smaller in diameter. However, these techniques are difficult to implement and practically impossible to utilize in a production environment.